Ab initio structure of the (Na2[CAl4])2 dimer.: Next step toward solid materials containing tetracoordinate planar carbon

We performed ab initio calculations on the (Na-2[CAI(4)])(2) dimer in order to test if the two CAI(4)(2-) groups react to form the more stable dimeric structure, or if the two CAl42- groups remain separated in a true dimeric structure. Working at the B3LYP/6-311+G* level of theory (previously found to be satisfactory in our earlier calculations with CAI(4)(-) and Na[CAI(4)](-)), we established that structures with the C-C bond are higher in energy than the structures with two isolated structural CAI(4)(-) units separated by more than 5 A with their structural and electronic integrity preserved. However, alternative structures involving reaction between two CAI(4)(2-) groups forming a C2Al84- cluster without the C-C bond are higher in energy, but they are still competitive with the true dimeric structure, While we found alternative structures of Na4C2Al8 with the energy comparable to that of the true dimeric structure, we hope that the solid ionic salt with the pentaatomic tetracoordinate planar carbon [CAI(4)](2-) building block can be synthesized.